The present invention relates generally to rotary machines, and more particularly to an actuated seal for a rotary machine such as a steam or gas turbine.
Rotary machines include, without limitation, turbines for steam plants and compressors and turbines for gas plants. A steam turbine has a steam path that typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path that typically includes, in serial-flow relationship, an air inlet, a compressor, a combustor, a turbine, and a gas outlet (also know as an exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, a gas path leakage in the turbine or compressor area of a gas turbine, between the rotor of the turbine or compressor and the circumferentially surrounding turbine or compressor casing, will lower the efficiency of the gas turbine thereby leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between the rotor of the turbine and the circumferentially surrounding casing, will lower the efficiency of the steam turbine thereby leading to increased fuel costs.
It is known in the art of steam turbines to position, singly or in combination, variable clearance labyrinth-seal segments, singly or in combination with at least one brush seal, in a circumferential array between the rotor of the turbine and the circumferentially surrounding casing to minimize steam-path leakage. Springs hold the segments radially inward against surfaces of the casing that establish radial clearance between the seal and rotor but allow segments to move radially outward in the event of rotor contact. While brush seals, singly or in combination with labyrinth-seal segments, have proved to be quite reliable, their ability to seal is decreased as a result of bending stresses on the bristles typically created by a pressure drop across the brush seal. Such bending stresses cause the bristles to bend, typically at the downstream portion of the bristle pack, thereby increasing the leakage of fluid therethrough.
Accordingly, there is a need in the art for a rotary machine having good leakage control between stationary and rotating components.
One embodiment of the present invention comprises a seal for controlling flow of a fluid in a fluid path in a rotary machine. The seal comprises a brush seal carrier having a front plate and a back plate disposed therein. A brush seal is disposed between the front plate and the back plate. In addition, a flexible member is disposed between the brush seal and the back plate for reducing stress in the brush seal.